What is the pressure change in this wash nozzle?

I have one question about the many wash nozzles.
The pump has 20 GPM @ 1000 PSI , the pipe size is 1" and connect 20 nozzles.
So the 1/4" nozzle may be 1GPM @ 1000 PSI. But the nozzle standard show the 1GPM is about 10 PSI.
and 1000psi need 10 GPM.
Can anyone know how to calculate the nozzle right pressure ?

I have one question about the many wash nozzles.
The pump has 20 GPM @ 1000 PSI , the pipe size is 1" and connect 20 nozzles.
So the 1/4" nozzle may be 1GPM @ 1000 PSI. But the nozzle standard show the 1GPM is about 10 PSI.
and 1000psi need 10 GPM.
Can anyone know how to calculate the nozzle right pressure ?

That depends on your pump characteristics. If your pump flows 20GPM regardless of pressure, you'll end up with only 10psi in your system, with each nozzle flowing 1GPM. If your pump flows more at lower pressure, you'll end up somewhere above 20GPM and somewhere between 10 and 1000psi. If you want 1000psi in your system, you'll either need a pump that flows 200GPM or nozzles that are much smaller. Alternatively, you could use a pair of your current nozzles and your current pump.